The long-range objective of the project is to delineate common and unique properties of avian coronavirus with respect to their biosynthetic strategy, their genetic behavior and their structural features. Major prototype strains of infectious bronchitis virus (IBV) will be comparatively studied to understand the molecular and genetic basis for their phenotypic differences and their evolution in nature as distinct antigenic variants. The technical approaches to be utilized include biochemical analyses of radiolabeled virions and viral gene products, development and characterization of conditional lethal mutants and electron microscopic examination of virions, subviral components and infected cells.